I'm trying to diagnose a fading out black toner problem. I've recently replaced the toner (dell branded), fuser, transfer roller but the problem has been unaffected. Suggestions on where to start? Colors always show up fine, but black can fade out completely but is usually worst at the center of the page.
Here's a scan of the gradient test:
I had the same problem, but now it's fixed. Take a look at this thread:
It starts out with a color problem, but read down and you can see how I fixed my black fading.